Optical discs such as compact discs have been widely used for recording and reproducing information. Compact discs can include a disc-shaped resin substrate made of polymethylmethacrylate resin or polycarbonate resin and an information recording layer having a pit on the surface of the disc-shaped resin substrate. A reflective layer and a protective layer may be sequentially formed on the surface of the information recording layer.
Compact discs can, however, have insufficient storage capacity. Accordingly, digital versified discs (DVDs) have been developed to increase storage capacity.
Generally, digital versified discs include two disc members including an active disc which records information and a dummy disc which protects the active disc. In contrast, a compact disc includes only a single disc.
The rotation speed for driving a DVD is about 10,000 rpm. Because the central core of the DVD is fixed during rotation and driving, the impact strength of the central core of DVD is very important. It can be especially important for the dummy disc, which protects an active disc, to exhibit crack resistance during driving or storage.
Polycarbonate or polymethylmethacrylate resins have been used as materials for the active disc. Polycarbonate resin has been conventionally used as the material for the dummy disc because of its good adhesion to an active disc, elongation, bending properties, and good impact resistance, which are all required properties for protecting an active disc.
However, polycarbonate resin is a relatively expensive resin, and thus its use can increase production costs of optical discs for DVDs. Further, because of its low flowability, polycarbonate resin requires high temperature and pressure during molding processes, which can decrease productivity.
If polymethylmethacrylate, SAN resin, or GPPS resin is used as a material for a dummy disc, although it is possible to form an optical disc by UV adhesion, these resins have reduced capability for protecting an active disc. As a result, problems such as a crack on the optical disc, may easily occur.
Furthermore, if ABS resin is used as a material for a dummy disc, although the dummy disc may have impact resistance, it may not be adhered by UV adhesion. Thus, an alternative method for adhesion other than UV adhesion may need to be adopted, which can result in addition processing steps.
Accordingly, the present inventors have developed an optical disc that has excellent flowability, strength, elongation and UV permeability as well as high productivity and may decrease production costs by employing a MABS resin as a dummy disc.